1. Field of the Invention
The present invention relates to an apparatus for performing bit stream transformation for re-coding a temporarily decoded input image signal under a prescribed system (such a series of decoding and re-coding are hereinafter collectively referred to as transcoding), and more particularly, it relates to an image signal transcoder capable of executing transcoding on an input bit stream as to an image signal coded under the MPEG2 standard or the DV standard.
2. Description of the Background Art
In recent years, data processing of image signals such as video data remarkably tends to digitization. While an important point of digital data processing of image signals is compression coding according to a signal compression technique, the standards of compression coding systems for image signals (hereinafter also referred to as image compression systems) are not necessarily unified.
One of representative standards is the MPEG2 (Moving Picture Experts Group 2) standard employed for a public set-top box (STB) capable of receiving and reproducing digital broadcasting, a DVD-Video which is a DVD (Digital Versatile Disc) for movie/music video works, a DVD-RTR which is a recording/reproducing DVD and the like. The MPEG2 standard is described in literature xe2x80x9cISO-IEC/JTC1 SC29 DIS13818, Part 2, 1994xe2x80x9d in detail.
A DVC (Digital Video Cassette) which is a public digital VTR employs a dedicated DV standard referred to as Mini DV as the image compression system. The DV standard is described in literature xe2x80x9cSD Specifications of Consumer-Use Digital VCRxe2x80x9d, HD Digital VCR Conference, December 1994, in detail.
Such digitization of image data processing is conceivably further expanded in the future in consideration of transition of TV broadcasting to digitization, accessibility to other devices indispensable to formation of a home network and the like.
Such progress in digitization of signal processing increasingly leads to the necessity for an application product capable of treating the aforementioned image compression systems in fusion, i.e., an application product receiving a bit stream formed under each coding standard, decoding the bit stream and re-coding the decoded bit stream according to a prescribed image compression system thereby enabling storage of image data between media having different coding standards, i.e., different image compression systems.
For example, application of a VTR receiving an input bit stream according to the MPEG2 standard corresponding to a set-top box (STB), transcoding the bit stream to a different bit rate and writing the bit stream in a recording/reproducing DVD (DVD-RTR) is assumable. Therefore, transcoding between bit streams of image data under different coding standards or between bit streams of image data having different bit rates under the same coding standard.
Both of the MPEG2 standard and the DV standard referred to as the representative coding standards, which are not reversible coding systems (lossless coding systems), are subjected to some distortion in the process of compression and expansion. Consequently, a decoded image based on a bit stream once coded is deteriorated in picture quality as compared with the source image. When re-coding the deteriorated image, the picture quality may be further remarkably deteriorated depending on the coding system.
An object of the present invention is to provide an image signal transcoder capable of performing transcoding while suppressing deterioration of picture quality between coding standards identical to or different from each other.
Briefly stated, the present invention provides an image signal transcoder temporarily decoding an input bits stream of coded image signal and re-coding the image signal under a prescribed system, comprising a decoding processing portion, a coding processing portion and a control portion.
The decoding processing portion decodes the input bit stream according to a prescribed coding standard and outputs decoded image data while extracting coding information of the input bit stream. The coding processing portion re-codes the decoded image data under the prescribed coding standard and forms an output bit stream. The control portion sets a coding parameter in the re-coding on the basis of the coding information.
According to another aspect of the present invention, an image signal transcoder temporarily decoding an input bits stream of coded image signal and re-coding the image signal under a prescribed system comprises a decoding processing portion, a coding processing portion and a control portion.
The decoding processing portion decodes the input bit stream according to a first coding standard and outputs decoded image data while extracting coding information of the input bit stream. The coding processing portion re-codes the decoded image data under a second coding standard and forms an output bit stream. The control portion sets a coding parameter in the re-coding on the basis of the coding information.
Accordingly, a principal advantage of the present invention resides in that the coding parameter in the re-coding is set on the basis of the coding information obtained when decoding the input bit stream and hence deterioration of the picture quality following transcoding between identical coding standards can be suppressed.
Further, the coding parameter in the re-coding under the second coding standard is set on the basis of the coding information obtained when decoding the input bit stream according to the first coding standard and hence deterioration of the picture quality following transcoding between different coding standards can be suppressed.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.